Cold formable valve steel

ABSTRACT

Cold formable, age hardenable, valve steel consisting essentially of 19-23% chromium, 4-6.5% nickel, 6.5-8% manganese, 0.15-0.30% each of carbon and nitrogen, up to 1% silicon, up to 0.2% columbium, up to 0.1% each of phosphorous and sulfur, balance iron, characterized as solution treated by low yield strength of under 75 ksi, low hardness of about 10-20 Rockwell &#39;&#39;&#39;&#39;C&#39;&#39;&#39;&#39; and high ductility, and being formable thence at temperatures below recrystallization into engine poppet valves and being age hardenable thence to maintain high ambient and elevated temperature hardnesses, high creep-rupture strength and low creep deformation, the steel having high corrosion resistance to leaded fuel exhaust gases, particularly at silicon contents of 0.2% and under.

United States Patent I 1191 EA/G/A/EER/A/G STRESS 6450) Kloske et al. Nov. 6, 1973 [5 COLD FORMABLE VALVE STEEL 2,799,577 1/1957 Schempp 75/128 A I 2,891,858 1/1959 Yeo 75/128 A [751 lnvemms- 9'? Khske, Parma Heights 3,284,250 11/1966 Kegerise 75/128 A William F. Barclay, Berea, both of Ohm Primary Examiner-Hyland Bizot [73] Assignee: Republic Steel Corporation, Attorney-Robert P. Wright et al.

Cleveland, Ohio [22] Filed: Sept. 17, 1971 {57] ABSTRACT [2]] Appl. No.: 181,399 Cold formable, age hardenable, valve steel consisting essentially of 19-23% chromium, 4-6.5% nickel, Apphcatlon Data 6.5-8% manganese, 0.150.30% each of carbon and [63] Cont1nuat1on-1n-part of Ser. No. 607,406, Jan. 5, nitrogen, up w 1% Silicon, up to 2 columbium, up 1967' to 0.1% each of phosphorous and sulfur, balance iron, characterized as solution treated by low yield strength U-So s n u u u A, N Cl. C17 and and being formable thence at [58] Field of Search 75/128 A, 128 N temperatures below recrystallization into engine pet valves and being age hardenable thence to maintain [56] Refverences cued high ambient and elevated temperature hardnesses,

. UNITED STATES PATENTS high creep-rupture strength and low creep deforma- 2,225,440 3/1965 Becket 75/128 A tion, the steel having high corrosion resistance to 3,152,934 10/1964 Lula 75/128 N leaded fuel exhaust gases, particularly at silicon con- 3,171,738 12/1940 Renshaw.... 75/128 N t t f (12% a d nder 3,401,036 9/1968 Dulis 75/128 A 2,495,731 l/1950 Jennings 75/128 A- 18 Claims, 3 Drawing Figures 1 SL'COAIIE/VT 0.27115. ms. EL. RA. HEAT 5 N0. SYMBOL (00 (m) (/60 (91,) ("/0 350 -0- 0,43 59.2 710.2 020 07.5

501 o /.20 02.7, /,0 50.5 00.0 3.42 I /-40. 01. z 71/. 500- 04.5

50.4 07/00 TREATED KZfi/k. Arz/00F, W/lTE/F QUE/VCHED o l I I l I IV ENG/NEER/NG STPA/A/ (00/10.)

ENG/NEZ-R/NG TENS/LE SZ'AESS-STRA/A/ BEHAVIOR OF SOZUT/ /V TEE/{TED 27-5-7 ALZOVS HAW/U6 V/Q/P/OUS 5L C'OIVTEA/TS PATENTED NOV 6 I973 SHEET 2 0F 3 SILICON CONTENT W770 @n EQQ E 2st 3% Qt B E EBEK VHP/AT/O/V OF THE SOLUTION TREATED TENS/LE ELOIVGAT/ON AA/D RE- DUCT/O/V Ml GEL-7) VALUES W/T S/L/CO/V CONTE/VZ INVENTORS R/C'HAPD A. KLOSKE WILLIAM F. BARCLAY MW: TQ Wt ATTORNEY COLD FORMABLE VALVE STEEL This application is a continuation-in-part of our copending application Ser. No. 607,406, filed Jan 5, 1967.

This invention pertains to steels especially adapted for use in exhaust valves for internal combustion engines, and provides a steel of novel composition and improved properties therefor, which is further characterized over steels which are presently commercially acceptable for such applications, 'in being coldformable, as by upsetting and extruding, into valve configuration.

The steel of the present invention is particularly adapted for use in exhaust valves for automobile engines, the required combination of room and elevated temperature properties for which are particularly severe. Typical minimum physical property requirements for a cold formable valve steel-for such applications are as follows: The elevated temperature rupture strength as measured by stress for 1% stretch at l,350 F. in 100 hours, should be 6,000 psi minimum, and as measured by stress for rupture at l,350 F. in 100 hours should be 10,000 psi minimum. As regards hardness, that at l,400 F. should be at least 90 Brinell, and at room temperature should be at least 27 Rockwell C. The oxidation resistance as measured by weight loss in grams per square decimeter per -hour (g/dmlhr),

should not exceed 60, as determined by heating a speci- Element Broad Preferred Chromium 19-23 20.5-21.5 Nickel 4.0-6.5 4.5-5.5 Manganese 6.5-8.0 7.0-8.0 Silicon -l .0 0-0.5 Carbon, 0 l-0.30 0.20-0.25 Nitrogen 0.15-0.30 0.20-0.25 C+N 0.40-0.50 Columbium 00.2 0.05-0 2 Phosphorous 0-0.l 0.04 Max Sulphur 0-0.'l 0.04 Max Balance Substantially Fe As discussed below the carbon content for valve applications should preferably be substantially equal to the nitrogen content within the limits for each above stated, and the total content of carbon plus nitrogen should preferably be between 0.4 and 0.5%. For optimum creep properties, the following ratio relationship of carbon-to-nitrogen should apply 1.0 s C/N s 1.2, with 0.22% each of carbon and nitrogen providing the optimum concentrations thereof. The preferred steel is of substantially the composition 2l%Cr-5%Ni-7%Mn- 0.2%C-0.2%N-(0-0.2)%Cb-Fe. The steel of the invention preferably contains columbium in amount of 0.05 to 0.2%. 1

The steel of the invention is of a balanced composition which is extremely critical with respect to the limits for each of the essential elements above specified. That is to say, our investigations have shown that the cold formability and other property requirements above stated, are obtained by so balancing the composition that the steel is completely austenitic or substantially so'at room temperature. Our investigations have furtherestablished that the critical structure-property relationships of the steel can be obtained only by carefully balancing the Ni, Mn, C and N values of the austenite.

The chromium content is set within critical limits of 19-23% and preferably '20.5-2l.5%, to assure adequate scale resistance and secondary hardening at service operating temperatures up to about l,400 F. When aged at about l,300-l,400 F, the steel undergoes secondary or age-hardening by precipitation of carbides and nitrides, and also phosphides, if the steel contains anappreciable amount of phosphorous. i.e., in

excess of about 0.04%. The sulphur content of the steel should not exceed about 0.1% and preferably should not exceed 0.04%.

Silicon, which is usually present as a residual element in these steels, may be employed in amounts up to about 1.0%, the preferred upper limit being about 0.5%, and should not exceed 0.20% where maximum oxidation resistance to leaded fuels is required.

While boron is not an essential constituent of these steels, it may be tolerated in residual amounts up to about 0.008%.

The nickel content'should be maintained as high as is commercially feasible to insure cold-formability. Our investigations indicate that the lower limit for nickel content on the basis of cold-formability requirements occurs at about 4%. Also that such increase in cold-formability as is obtained with nickel contents in excess of about 6 to 6.5%, is insufficient to warrent the increase in alloy costs.

Neither high nickel nor nickel-plus-manganese is employed or required in applicants steel for imparting an austenitic structure, this being achieved more efficiently and cheaply by the relatively high contents of the interstitials, carbon and nitrogen. Thus applicants steel differs fundamentally in this respect from low carbon austenitic steels of, for example, 0.05% max. carbon, which are strengthened exclusively by nitrogen additions, and which require a minimum of about 14% nickel plus'manganese for imparting a fully austenitic structure, and also a minimum of about 8% manganese for preventing ingot porosity. in applicants steel manganese is employed primarily for maintaining a high nitrogen' content in the steel as an austenitizing agent.

' the austenite, thereby correspondingly reducing the cold formability of the steel, it should preferably conabove discussed, compositions according to the following Table I were melted and thereafter tested as discussed below.

4 these steels had aged room temperature hardnesses in the range of -39 Rc (Rockwell C"), well in excess of the specified minimum of 27 Re. It will further be TABLE l.-NOM1NA1. AND ANALYZED COMPOSITIONS OF THE EXPERIMENTAL COLD FORMING VALVE STEELS (21-5-7/Cr-Ni-Mn steels: Varying C,N,P.Cb content) Alloy content (weight percent) Cr Ni Mn Si C N P Cb C N N designates the nominal composition and A the actual composition.

Specimens of each of the above steels were tested for 30 noted that these steels had by far the lowest creep hardness, creep strain and impact strength in various heat-treated and otherwise processed conditions, with results as shown in the following Table II. N designates the nominal composition and A the actual composition.

strain values within the range of 0.15-0.29%, far below the specified minimum of 1% stretch in 100 hours at 6,000 psi. From the Table II data it will be seen that the I aforesaid steels of this invention had far less than a 1% TABLE ll.-MECHANICAL PROPERTIES OF THE EXPERIMENTAL COLD FORMING VALVE STEELS (21-5-7/Cr-Ni-Mn steels with varying C, N, P, Cb, A1 contents) Creep strain Hardness Rockwell C' 1,350 F Nominal alloy content 10,000 psi 1.400 F F (weight percent) Cold rolled Aged (at 1,350 F) percent Brinell impact Solution 50 percent strain/test hardness strength Heat No. C N Other treated reduction 100 h 1,000 h duration. h BHN ft-lbs.

B40 0.2 12.3 41.8 39.8 38.3 17.0/ 96.6 4 B51 .2 12.1 44.6 40.0 38.4 057/100 124.5 4 B41 .4 23.5 48.2 34.9 33.5 24.2/57 108.9 17 B52... .3 17.1 45.4 34.8 34.6 24.3/93 97.2 9 B53... .2 12.4 44.9 37.9 35.7 0.29/100 128.3 8 B54... .2 16.0 45.1 37.5 35.7 0.15/100 135.4 8 B42... .15 12.9 39.9 37.7 37.4 19.2/26 97.2 4 312.... .15 14.0 43.0 37.0 36.5 163/100 114.0 6 313.... .25 13.0 40.0 36.0 35.5 02/100 121.0 5 314.... .25 16.0 42.0 39.0 39.0 02/100 139.0 5 315 .25 15.0 0.2/100 147.0 5

Solution treatment: 1 h at 2.050 F. water quenched.

=(reep sample thermo'mechanical history: solution treated as in (1) above. ground to 0.750-in. dia., cold rolled to 0.5-in. thickness in 2 passes. stress relief annealed 2 h at 1,350 F.

From the above data it will be seen that although all of the above steels meet most of the above-stated minimum requirements for the ideal steel for automobile engine exhaust valves, only steels B53, B54, 313, 314 and 315 meet all of the requirements as regardsminimum room and elevated temperature hardness, creep strain and impact strength, these being the steels in which the carbon and nitrogen contents were substantially equal within the range of about 0. 1 50.25% each, and C+N within limits of 04-05%, as shown by the actual compositions of Table I. It will be observed that "Hardness, impact sample thermo-mechanical history: same as. (2) above, aged 98 h at 1.350 F.

BHN. 1,000 kg load, 10 mm dia. chromium carbide indenter.

creep strain after 100 hours at the much higher stress of 10,000 psi. In addition, the above mentioned steels had by far the highest 1,400 F hardness values of 121 to 147 BHN, well above the specified minimum of BHN. Also these steels had a creep-rupture life of more than hours as stressed at 1,350 Fand 10,000 psi.

Since all of these steels were melted to a nominal composition of 2l%Cr-5%Ni-7%Mn with varying amounts of carbon and nitrogen plus in some instances optional additions of phosphorous and columbium, the test data clearly demonstrates the critical effects of the as evidenced by the data for steels B53, B54 and 313-315 inc.

Room temperature tensile properties of the aboveidentified steels in the condition as solution treated at about 2,100 F. and water quenched are shown in the following Table 111.

TABLE Ill TENSILE PROPERTIES OFNOMINAL 2lCr-5Ni-7Mn STEEL WITH VARYING C, N, P, Cb

Heat Alloy Content 0.2%Y.S. U.T.S. El RA No. (wt. (ksi) (ksi) B41 0 4 C-0.2 N 74.5 129.8 38.5 47.5 B52 0.3 C-0.l N 58.6 117.3 47.0 53.3 B53 0.2 C-0.2 N 59.7 113.5 55.5 59.1 B42 015 -0.1 N 57.6 102.5 52.0 67.2 854 0.2 C-0.2 N-0.07 Cb 63.4 116.4 53.5 65.2 B51 0.2 C0.2 N-0.1 P 59.1 110.9 58.5 64.8 B40 0.2 C-0.03 N-0.l P 52.1 102.6 46.5 57.5 312 0.15 C-0.25 N 68.7 128.4 51.5 61.0

without difficulty. However, for cold upsetting and extrusion into internal combustion engine valves, the steels having area reductions of at least about 60% with low yield strengths, were found most suitable as closely approximating the cold formability of type 305 stainless steel, the annealed properties of which are 37,000 psi yield and 85,000 psi tensile strength, with 55% elongation in 2 inches and 65% area reduction. As shown by Table 111 the steels most closely approximating these values as regards low yield strength and high area reduction values are steels B42, B51, B53, B54 and 313-315 inc. As shown above in Table 1, however, only steels B53, B54 and 313-315 inc. of this group meet the combined minimum requirements as to creep strain and impact strength for valve applications although all are excellent steels for other applications.

As regards corrosion resistance to the exhaust gases of leaded fuels, steel B-B42 inc., B54 and 313-315 inc. werefound to have corrosion rates of less than 60 g/dm IhL, and thus within the acceptable range for the ideal automotive valve steel in this respect. Hence all of steels B54 and 313-315 inc. met all of the minimum requirements for the ideal valve steel.

Reverting to Table I, all steels thereof contained about 1/2% silicon, a residual of variable content in most steels. In order therefore to determine the effects on mechanical properties and leaded fuel corrosion resistance of varying the silicon content in the steel of this invention, steels of the compositions shown in the following Table IV were melted.

TABLE lV.-A1M AND ANALYZED CHEMICAL COMPOSITIONS OF THEZl-5-7 ALLOYS HAVING VARIOUS SlLlCON CONTENTS EMPLOYED IN THE MECHANICAL PROPERTY AND LEAD OXIDE CORROSION EVALUATION PROG RAMS Heat No. Cr Ni Mn Si Cb C N (1+ N (a) Aim compositions for heats:

B358/B362 21.00 5.0 7 0 0.50/1.50' 0.07 0.21 0.21 0.42 (b) Analyzed compositions:

B358 20.85 5.1 7.0 0.43 0.09 0.19 0.19 0.38 20.95 5.1 7.0 0.67 0.08 0.19 0.18 0.37 20.20 5.0 7 0 0.88 0.08 0.19 0.18 0.37 20.85 5.1 7 0 1.20 0.08 0.18 0.17 0.35 20.35 5.0 6 6 1.40 0.08 0.18 0.18 0.36 (a)Aim Compositions for heats:

3705/8709. V942 21.00 5.4 7.25 f-0.00/0.75 0.11 0.24 0.20 0.44 (b) Analyzed compositions: B705 21.60 5.7 7.65 0.74 0.13 0.30 0.23 0.53 21.55 6.0 7.45 0.60 0.13 0.26 0.21 0.47 21.40 5.8 7.60 0.42 0.12 0.21 0.20 0.41 21.40 5.8 7.50 0.27 0.13 0.24 0.20 0.44 21.40 5.6 6.90 0.19 0.13 0.27 0.22 0.49 V942 21.00 5.2 7.10 0.02 0.12 0.26 0.22 0.48

1 In 0.25 percent increments. 2 ln 0.15 percent increments.

313 0.25 00.15 N 59.7 113.2 61.5 60.0 The solution treated mechanical properties of these 314 0.25 C-0.25 N 63.2 113.6 58.5 69.5 315 0.25 00.25 N 64.2 "3.8 600 710 steels are tabulated and plotted agalnst slllcon content latter as measured both by elongation and area reduc- 65 tion, conducive to good cold forming properties. As shown by Table II, these-steels reduced by cold rolling in FIGS. 1 and 2 of the accompanying drawings; while .the corrosion rates thereof in molten l 'B O at l,675

F are similarly plotted in FIG. 3.

As shown in FIGS. 1 and 2, silicon up to about 0.7% exerts very little influence on the mechanical properties of the steel, but above this results in loss of ductility in the solution treated conditions.

Referring to FIG. 3, the silicon content has a marked effect on the corrosion rate in molten lead oxide, tending toward a maximum at silicon contents centered about 0.5% Si, with reductions at higher and lower Si levels, but tending toward a minimum as the Si content approaches zero. At all Si levels, however, the corrosion rate is well under the above spcified limit of 60 gldm lhr. At Si contents of about 0.2% and under the corrosion rate for the steel of this invention is less than 20 g/dmlhr and compares favorably with the corrosion rates for the best of the prior art valve steels shown.

Although the steels of the invention are cold formable into valves at room temperature, the required forming pressures are greatly reduced by preheating to about 450-l,600 F, i.e. below the recrystallization temperature, prior to forming, the preferred temperature range being about 1,200-1,300 F, which might properly be termed warm forming in contrast to the conventional hot forming of valve steels at a forging heat of about 1,9002,200 F.

Steels according to the invention are preferably produced by melting the ingredients in the electric arc furnace, teeming in a molten state into ladles, followed by casting into ingot molds. The stripped ingots are reheated to about l,9002,200 F, and for valve applications, hot rolled into bars and air-cooled to room temperature. For cold or warm extrusion, the bars are solution treated at 2,0502,l50 F, preferably 2,100 F, usually for about one hour or until allcarbides are in solution, and thereupon cooled to room temperature with sufficient rapidity, as by water quenching, to retain carbides in solution, in which state the hardness is about 1020 Re. The bar stock is then cut into lengths for valve components and cold or warm upset into valve shapes, the resultant hardness being about 4050 Rc. The valves are then stress-relieved at about 1,3001,400 F, preferably at 1,350" F, for about 2 hours and air cooled to room temperature, the resulperature. As the following discussion will show, the carbon and nitrogen content of the applicants steel critically affects the microstructural changes accompanying aging and, hence, the mechanical properties of the aged steel.

At a carbon content of about 0.3% or greater, much of the carbide phase of the steel remains undissolved after the solution treatment anneal. On aging at 1,350 F. after cold reduction, the dissolved carbon precipitates at slip bands and as large globular particles randomly dispersed throughout the austenite. These modes of precipitation impart resistance neither to softening nor to deformation by creep at the service temperature. Thus, a high concentration of undissolved carbides leads to an ineffective precipitate structure.

A total carbon plus nitrogen content of less than about 0.3% is insufficient to maintain a completely austenitic structure in these steels. Consequently, some delta ferrite is present in their microstructure after solution treatment. During aging after cold forming, carbides precipitate preferentially within these ferrite bands leaving the austenite matrix relatively depleted of precipitate particles. Although this banding of the precipitate phase results in a high hardness which is stable at 1,350 F, it presents no obstacle to deformation by creep in the precipitate-poor austenite. On the other hand, a solution treated steel of the invention containing about 0.2% each of carbon and nitrogen is found to completely dissolve the carbide phase without introducing large amounts of high temperature ferrite.

The following Table V gives the melting range and actual compositions of a series of production heats of steels according to the invention.

TABLE V. MELTING RANGE CHEMICAL COMPOSITION AND LADLE ANALYSES OF THE 2157 PRODUCTION HEATS Alloy content (wt.

Residual elements (wt.

Heat No. Cr Ni Mn Si Cb C N (C+N) Cu Mo Al P S Mam". ran 6 {20.75 5.0 7.0 0.18 0.05 0.22 0.16 0.40 0.50 0.04 .0. g 21.25 5.5 8.0 0.25 0.15 0.26 0.20 min. max. max max. 3331227 20.7 5.45 7.25 0.50 0.13 0.24 0.17 0.41 0.24 0.24 0.020 0.032 0.007 8043073... 20.9 5.50 7.10 0.64 0.09 0.25 0.19 0.44 0.31 0.24 0.035 0.035 0.008 8043078... 20.9 5.35 7.25 0.61 0.11 0.25 0.19 0.44 0.21 0.19 0.035 0.028 0.013 8043344... 21.4 5.60 7.40 0.69 0.12 0.24 0.19 0.43 0.18 0.26 0.030 0.033 0.006 8043363... 21.0 5.50 7.40 0.57 0.10 0.23 0.18 0.41 0.19 0.33 0.030 0.033 0.005 8043601 21.1 5.50 7.10 0.13 0.09 0.22 0.21 0.43 0.21 0.22 0.040 0.030 0.006 8043666... 21.1 5.35 7.45 0.20 0.11 0.22 0.19 0.41 0.20 0.24 0 025 0.035 1 0.005 8054313... 21.0 5.45 7.45 0.22 0.08 0.23 0.19 0.42 0.36 0.27 0.050 0.038 0009 8044254.... 20.8 5.40 7.40 0.31 0.12 0.24 0.23 v 0.47 0.21 0.51 0.030 0.034 0007 8044541 21.0 5.40 7.40 0.28 0.11 0.24 0.21 0.45 0.26 0.28 0.030 0.029 0.007

tant hardness being at least Rc. The valves are The Table V steels were produced by air melting in placed in service in automobile engines having a seran electric arc furnace. The requisite interstitial elevice temperature for exhaust valves of about 1,350 F. ment content of the alloy was derived from additions of While in service the valves undergo secondary or age high-carbon scrap or ferrochromium and high-nitrogen hardeni h as to maintain th room t at chromium, manganese or their ferroalloys. Columbium was added in the form of ferrocolumbium. The nominal hardness about 30 Rc.

With the exception of the ability to be cold formed into a finished piece, the most severe mechanical property requirement a cold forming valve steel must satisfy, is the ability to resist further deformation by creep at the intended service temperature. The major alloy design problem is economically to utilize the residual strengthening resulting from the forming operation together with precipitation hardening at the service temperature to transform a steel having good cold forming characteristics at lower temperatures into one which will resist deformation at an intermediate temperature.

To achieve such a transformation in properties, a favorable structural revision must occur at the service temmanganese content of 7% appears to be sufficient to contain the 0.20/0.25% N in both the liquid and solid steel.

With regard to the residual elements in the Table V steels, the reduction in silicon content initiated in heat number 8,043,601 was designed to improve lead oxide corrosion resistance to the aforementioned value of 2 0 g/dm /hr. Copper, an austenite promoter, and the ferrite promoting element, molybdenum, are the major residual elements and are present in roughly equivalent concentrations between 0.18 and 0.51%. Phosphorous is present in a narrow range between 0.028 and 0.038% and the S content ranges between 0.005 and 0.013%.

Random checks show the Co content to be of the order of 0.07%. Important to the hot workability of the alloy are its Sn and Pb contents which have attained maximum values of 0.028 and 0.003%, respectively. Examination of Table V shows that the nominal 0.02% A1 content of the steel has actually been as high as 0.050% in heat number 8,054,313. Lastly, determinations of the O and B, made only in heat number 3,331,227, show these elements to be present in amounts of 0.003 and 0.002%, respectively.

Table VI below summarizes the tensile properties measured in samples of alloy heat number 3,331,227 after various processing options. perusal-of this table clearly shows formability properties of the, cold drawn and annealed alloy to exceed those of the hot rolled alloy annealed at the same temperature. In general, samples of the cold drawn alloy water quenched after .annealing for 30 minutes at 2,100" F exhibited the following nominal mechanical properties:

0.2% offset yield strength: 55/60 ksi ultimate tensile strength: 110/120 ksi elongation (in 2-in.): 60/65% reduction in area: 70/75% Charpy V-notch impact strength: 230/260 ft-lbs Rockwell B hardness: 90/100 elongation of at least an area reduction at least 50%, and in being deformable by upsetting and extrusion below its recrystallization temperature, and being hardenable up to at least 35 Rockwell C" by deformation and aging at about l,350 F, and by a Brinnel hardness as aged of at least 100 at l,400 F.

3. An age hardenable, cold formable, austenitic alloy steel consisting essentially of: 19 to 23% chromium, 4.5 to 6.5% nickel, 6.5 to 8.0% manganese, 0 to 0.5% silicon, 0.20 to 0.25% each of carbon and nitrogen, up to 0.2% columbium, up to 0.04% each of phosphorous and sulphur, up-to 0.008% boron, and the balance iron, the carbon content being substantially equal to the nitrogen content, said steel having at room temperature, a Rockwell C hardnesses of under 20 as solution treated and quenched and in being deformable by upsetting and extrusion below its recrystallization temperature, and by a hardness of at least 35 Rockwell C as thereafter deformed and aged at about l,350 F., a hardness of at least 100 Brinell at l,400 F, and a creep deformation of under 0.6% when stressed at 10,000 psi for 100 hours at l,350 F.

4. An age hardenable, cold formable, austenitic alloy steel consisting essentially of: 19 to 23% chromium, 4.5 to 5.5% nickel, 6.5 to 8.0% manganese, up to 0.5% sili- TABLE VI.TENSILE PROPERTIES OF 21-5-7 PRODUCTION HEAT NUMBER 3331227 AFTER VARIOUS PROCESSING OPTIONS 0.2 percent 1 Ultimate offset yield tensile Elongation Reduction strength strength (percent in in area Material condition (ksi) (ksi) 2-in.) (percent) HR 67 1 17 52 66 HR. ST (2.000 F) 66 117 54 67 HR.ST (2,050 F)....... 64 117 57 69 HR.ST(2.100 F).... 56 111 67 74 HR, CI) (8.3% RA). 95 127 37 59 HR.ST.CD 74 120 53 74 HR. CD, ST (2.000 61' I14 59 72 HR, CD. ST (2.050 F). 58 113 61 74 HR,CD, ST (2,100 F). 64 Ill 62 75 HR.CD. ST 51 I02 68 76 HR hot rolled. ST solution treated. CI) cold drawn.

What is claimed is: con, 0.15 to 0.3% each of carbon and nitrogen, the

-I. An age hardenable, cold formable alloy steel consisting essentially of about: 19 to 23% chromium, 4.0 to 6.5% nickel, 6.5 to 8.0% manganese, 0 to 1.0% silicon, 0.15 to 0.3% each of carbon and nitrogen, up to 0.2% columbium, 0 to 0.1% each of phosphorous and sulphur, up to 0.008% boron, and the balance iron, characterized by Rockwell C hardnesses of under 20 as solution treated at 2,050 F. and quenched, and in being deformable by upsetting and extrusion below its recrystallization temperature, and by a Rockwell C hardness of at least 35 as thereafter deformed and aged at l,350 F., and by a Brinell hardness as aged of at least 100 at l,400 F.

2. An age hardenable, cold formable alloy steel consisting essentially of: 19 to 23% chromium, 4.0 to 6.5% nickel, 6.5 to 8.0% manganese, up to 0.7% silicon, 0.15 to 0.25% each of carbon and nitrogen, up to 02% 'columbium, up to 0.1% each of phosphorus and sulphur, up to 0.008% boron, and the balance iron, the carbon content of said steel being at least equal to the nitrogen content, said steel having at room temperature as solution treated at about 2,100 F. and quenched, a 0.2%

-offset yield strength of not over 75,000 psi, a tensile total carbon and nitrogen content being 0.4 to 0.5%,up to 0.2% columbium, up to 0.1% each of phosphorous and sulphur, up to 0.008% boron, and the balance iron, carbon being at least equal to the nitrogen content, said steel having at room temperature as solution treated and quenched, a 0.02% offset yield strength of not over ksi, a tensile elongation of at least 50%, an area reduction of at least 50% and being extrudable and upsetable at temperature not exceeding l,600 F, and in being age hardenable thence up to at least 35 Rockwell C, said steel having a corrosion rate in molten lead oxide at l,675 F. of less than 60 g/dm /hr., and in a Brinnel hardness as aged of at least at 1,400 F.

5. An age hardenable, cold formable, austenitic alloy steel consisting. essentially of about: 20.5 to 21.5% chromium, 4.5 to 5.5% nickel, 7 to 8% manganese, up to 0.2% silicon, 0.15 to 0.25% each of carbon and nitrogen, up to 0.2% columbium, sulphur and phosphorous not over 0.04% each, up to 0.008% boron, and the balance iron, said steel as solution treated at 2,050 F i and quenched being extrudable and upsetable at temperatures of not over l,600 F., and by a Rockwell C hardness of at least 35 as thereafter cold reduced and aged at l,350 F., a Brinnel hardness of at least 100 at l,400 F. and having a corrosion loss in molten lead oxide of not over 20 gldm /hr. 1

6. An age hardenable, cold formable, austenitic alloy steel consisting essentially of: 20.5 to 21.5% chromium, 4.5 to 5.5% nickel, 7 to 8% manganese, up to 0.5% silicon, 0.2 to 0.25% carbon, 0.2 to 0.25% nitrogen, up to 0.2% columbium, sulphur and phosphorous not over 0.04% each, up to 0.008% boron, and the balance iron, the carbon content being related to the nitrogen content in accordance with the ratio 1 S C/N s 1.2.

7. An age hardenable, cold formable, austenitic alloy steel consisting essentially of: 20.5 to 21 .5% chromium, 4.5 to 5.5% nickel, 7 to 8% manganese, up to 0.9% silicon, 0.2 to 0.25% carbon, 0.2 to 0.25% nitrogen, 0.05 to 0.2% columbium, sulphur and phosphorous not over 0.04% each, up to 0.008% boron, and the balance iron, with carbon at least equal to the nitrogen content.

8. An age hardenable, cold formable, austenitic alloy steel consisting essentially of about: 21% chromium, nickel, 7% manganese, up to 0.5% silicon, 0.2 to 0.25% carbon, 0.2 to 0.25% nitrogen, up to 0.2% columbium, sulphur and phosphorous not over 0.04% each, up to 0.008% boron, and the balance iron.

9. Internal combustion engine valves and valve components made of an alloy steel according to claim 1.

l0. lntemal combustion engine valves and valve components made of an alloy steel according to claim 2.

ll. lntemal combustion engine valves and valve components made of an alloy steel according to claim 3.-

12. Internal combustion engine valves and valve components made of an alloy steel according to claim 4.

13. Internal combustion engine valves and valve components made of an alloy steel according to claim 5.

l4. lntemal combustion engine valves and valve components made of an alloy steel according to claim 6.

15. Internal combustion engine valves and valve components made of an alloy steel according to claim 7.

16. Internal combustion engine valves and valve components made of an alloy steel according to claim 8.

17. lntemal combustion engine valves and valve components made of an age hardened alloy steel consisting essentially of about: 19-23% chromium, 4.06.5% nickel, 6.58.0% manganese, 0.l50.30% each of carbon and nitrogen, 0-l0% silicon, 0-O.2% columbium, 0-0.l% each of phosphorous and sulphur, balance iron, said steel having at room temperature, a Rockwell C hardness of at least 35, a Charpy V notch impact strength of at least 5 ft.lbs, a Brinnel hardness of at least at l,400 F.

18. lntemal combustion engine valves and valve components made of an age hardened, austenitic, alloy steel consisting essentially of about: 20.5-21.5% chromium, 4.55.5% nickel, 7.08.0% manganese, O.200.25% each of carbon and nitrogen, the total carbon and nitrogen content being 0.40O.50%, 00.5% silicon, 0.05-0.20% columbium, 00.04% I each. of phosphorous and sulphur, balance iron, said steel having a Rockwell C hardness at room temperature of at least 35 Rockwell C, a Charpy V notch impact strength of at least 5 ft.lbs. and a Brinnel hardness of at least 100 at l,400 F. 

2. An age hardenable, cold formable alloy steel consisting essentially of: 19 to 23% chromium, 4.0 to 6.5% nickel, 6.5 to 8.0% manganese, up to 0.7% silicon, 0.15 to 0.25% each of carbon and nitrogen, up to 0.2% columbium, up to 0.1% each of phosphorus and sulphur, up to 0.008% boron, and the balance iron, the carbon content of said steel being at least equal to the nitrogen content, said steel having at room temperature as solution treated at about 2,100* F. and quenched, a 0.2% offset yield strength of not over 75,000 psi, a tensile elongation of at least 35%, an area reduction at least 50%, and in being deformable by upsetting and extrusion below its recrystallization temperature, and being hardenable up to at least 35 Rockwell ''''C'''' by deformation and aging at about 1,350* F, and by a Brinnel hardness as aged of at least 100 at 1,400* F.
 3. An age hardenable, cold formable, austenitic alloy steel consisting essentially of: 19 to 23% chromium, 4.5 t0 6.5% nickel, 6.5 to 8.0% manganese, 0 to 0.5% silicon, 0.20 to 0.25% each of carbon and nitrogen, up to 0.2% columbium, up to 0.04% each of phosphorous and sulphur, up to 0.008% boron, and the balance iron, the carbon content being substantially equal to the nitrogen content, said steel having at room temperature, a Rockwell ''''C'''' hardnesses of under 20 as solution treated and quenched and in being deformable by upsetting and extrusion below its recrystallization temperature, and by a hardness of at least 35 Rockwell ''''C'''' as thereafter deformed and aged at about 1, 350* F., a hardness of at least 100 Brinell at 1,400* F, and a creep deformation of under 0.6% when stressed at 10,000 psi for 100 hours at 1,350* F.
 4. An age hardenable, cold formable, austenitic alloy steel consisting essentially of: 19 to 23% chromium, 4.5 to 5.5% nickel, 6.5 to 8.0% manganese, up to 0.5% silicon, 0.15 to 0.3% each of carbon and nitrogen, the total carbon and nitrogen content being 0.4 to 0.5%, up to 0.2% columbium, up to 0.1% each of phosphorous and sulphur, up to 0.008% boron, and the balance iron, carbon being at least equal to the nitrogen content, said steel having at room temperature as solution treated and quenched, a 0.02% offset yield strength of not over 75 ksi, a tensile elongation of at least 50%, an area reduction of at least 50% and being extrudable and upsetable at temperature not exceeding 1,600* F, and in being age hardenable thence up to at least 35 Rockwell ''''C'''', said steel having a corrosion rate in molten lead oxide at 1,675* F. of less than 60 g/dm2/hr., and in a Brinnel hardness as aged of at least 100 at 1,400* F.
 5. An age hardenable, cold formable, austenitic alloy steel consisting essentially of about: 20.5 to 21.5% chromium, 4.5 to 5.5% nickel, 7 to 8% manganese, up to 0.2% silicon, 0.15 to 0.25% each of carbon and nitrogen, up to 0.2% columbium, sulphur and phosphorous not over 0.04% each, up to 0.008% boron, and the balance iron, said steel as solution treated at 2,050* F and quenched being extrudable and upsetable at temperatures of not over 1,600* F., and by a Rockwell ''''C'''' hardness of at least 35 as thereafter cold reduced and aged at 1,350* F., a Brinnel hardnEss of at least 100 at 1,400* F. and having a corrosion loss in molten lead oxide of not over 20 g/dm2/hr.
 6. An age hardenable, cold formable, austenitic alloy steel consisting essentially of: 20.5 to 21.5% chromium, 4.5 to 5.5% nickel, 7 to 8% manganese, up to 0.5% silicon, 0.2 to 0.25% carbon, 0.2 to 0.25% nitrogen, up to 0.2% columbium, sulphur and phosphorous not over 0.04% each, up to 0.008% boron, and the balance iron, the carbon content being related to the nitrogen content in accordance with the ratio 1 < or = C/N < or = 1.2.
 7. An age hardenable, cold formable, austenitic alloy steel consisting essentially of: 20.5 to 21.5% chromium, 4.5 to 5.5% nickel, 7 to 8% manganese, up to 0.9% silicon, 0.2 to 0.25% carbon, 0.2 to 0.25% nitrogen, 0.05 to 0.2% columbium, sulphur and phosphorous not over 0.04% each, up to 0.008% boron, and the balance iron, with carbon at least equal to the nitrogen content.
 8. An age hardenable, cold formable, austenitic alloy steel consisting essentially of about: 21% chromium, 5% nickel, 7% manganese, up to 0.5% silicon, 0.2 to 0.25% carbon, 0.2 to 0.25% nitrogen, up to 0.2% columbium, sulphur and phosphorous not over 0.04% each, up to 0.008% boron, and the balance iron.
 9. Internal combustion engine valves and valve components made of an alloy steel according to claim
 1. 10. Internal combustion engine valves and valve components made of an alloy steel according to claim
 2. 11. Internal combustion engine valves and valve components made of an alloy steel according to claim
 3. 12. Internal combustion engine valves and valve components made of an alloy steel according to claim
 4. 13. Internal combustion engine valves and valve components made of an alloy steel according to claim
 5. 14. Internal combustion engine valves and valve components made of an alloy steel according to claim
 6. 15. Internal combustion engine valves and valve components made of an alloy steel according to claim
 7. 16. Internal combustion engine valves and valve components made of an alloy steel according to claim
 8. 17. Internal combustion engine valves and valve components made of an age hardened alloy steel consisting essentially of about: 19-23% chromium, 4.0-6.5% nickel, 6.5-8.0% manganese, 0.15-0.30% each of carbon and nitrogen, 0-10% silicon, 0-0.2% columbium, 0-0.1% each of phosphorous and sulphur, balance iron, said steel having at room temperature, a Rockwell ''''C'''' hardness of at least 35, a Charpy V notch impact strength of at least 5 ft.lbs, a Brinnel hardness of at least 100 at 1,400* F.
 18. Internal combustion engine valves and valve components made of an age hardened, austenitic, alloy steel consisting essentially of about: 20.5-21.5% chromium, 4.5-5.5% nickel, 7.0-8.0% manganese, 0.20-0.25% each of carbon and nitrogen, the total carbon and nitrogen content being 0.40-0.50%, 0-0.5% silicon, 0.05-0.20% columbium, 0-0.04% each of phosphorous and sulphur, balance iron, said steel having a Rockwell ''''C'''' hardness at room temperature of at least 35 Rockwell ''''C,'''' a Charpy V notch impact strength of at least 5 ft.lbs. and a Brinnel hardness of at least 100 at 1,400* F. 